1. Field of the Invention
The present invention relates to an apparatus and a method of sending/receiving an OFDM signal, and more particularly, for example, to a transmission beam forming method.
2. Related Art
An example of a transmission beam forming scheme for an OFDM signal is a scheme for calculating reception weights (amplitude and phase) for combining signals from respective antennas at a maximum ratio in such a way that a signal-to-noise power ratio of a received signal reaches a maximum for each subcarrier and using these reception weights as transmission weights (e.g., see JP-A 2002-368714 (Kokai)).
According to a transmission beam forming method based on such a conventional OFDM scheme, when behavior of noise and interference varies from one subcarrier to another, if weights used for reception combining are applied as transmission weights as is, a delay profile (time response) of a channel is temporally extended considerably, resulting in a problem that the delay profile does not fall within a guard interval.
Furthermore, when pilots do not exist in all subcarriers, interference occurs due to influences of aliasing (overlap), resulting in a problem that a receiver cannot estimate the channel correctly.